A prior art automobile driving system including a longitudinal arrangement of an engine and a transmission is disclosed in JP-A No. 51-89066. As shown in FIG. 1, this prior art automobile driving system is of a substantially U-shaped drive line in which an engine 1001, a torque converter 1002 and a belt-drive variable-speed transmission 1003 are disposed coaxially in a longitudinal arrangement, a reverse gear 1004 including a planetary gear is interposed between the torque converter 1002 and the belt-drive variable-speed transmission 1003, and power is transmitted from the belt-drive variable-speed transmission 1003 through a drive shaft 1006 to a differential gear 1005 disposed under the engine 1001.
This automobile driving system, however, has a relatively great length along the longitudinal axis of the vehicle body because the engine 1001, the torque converter 1002, the reverse gear 1004 and the transmission 1003 are arranged coaxially in a longitudinal arrangement. Therefore, a rear portion of the automobile driving system interferes with the wall of a tunnel formed under a passenger chamber in the vehicle body when the automobile driving system is installed in an engine room and hence the wall of the tunnel must be unavoidably protruded into the passenger chamber. Furthermore, a toe board separating the engine room and the passenger room from each other unavoidably needs to be shifted toward the passenger room, which reduces the space of the passenger room, adversely affecting the comfortability of the passenger room. Since the automobile driving system is disposed close to the toe board, the passenger room needs to be further reduced to secure a sufficient crush stroke for safety in case of head-on collision, which further spoils the comfortability of the passenger room. Moreover, it is difficult to secure a sufficient working space in the engine room which makes work for installing the automobile driving system in the engine room and maintenance work difficult.
In an automobile driving system shown in FIG. 2 proposed to solve the foregoing problems, a torque converter 1002 and a belt-drive variable-speed transmission 1003 are disposed coaxially behind an engine 1001 in a longitudinal arrangement. A reverse gear 1004 and a differential gear 1005 are disposed under the engine 1001, and the output driving force of the transmission 1003 is transmitted through the reverse gear 1004 and a drive shaft 1006 to the differential gear 1005. Thus, the length a of the automobile driving system along the axis of the vehicle is relatively small.
Although the disposition of the reverse gear interposed between the torque converter and the belt-drive variable-speed transmission under the engine is effective in reducing the length a along the longitudinal axis of the vehicle, the overall height h of the automobile driving system increases as shown in FIG. 2. The automobile driving system having such a relatively great overall height h imposes restrictions on the design of a slant nose body and limits the freedom of vehicle body design.
The foregoing prior art automobile driving systems are intended for use on a two-wheel drive vehicle. A center differential gear must be interposed between the reverse gear and the differential gear when constructing a automobile driving system for a four-wheel drive vehicle on the basis of those prior art automobile driving systems to distribute the output driving force of the reverse gear to the front and the rear axles. Consequently, a portion of the gear train lying under the engine protrudes greatly downward and the automobile driving system has a complicated construction.
Accordingly, it is an object of the present invention to solve the foregoing problems in the foregoing prior art automobile driving systems and to provide a compact automobile driving system having relatively small longitudinal and transverse dimensions, increasing the degree of freedom of vehicle body design, and securing a space for crush stroke and driving system mounting and dismounting work.
Another object of the present invention is to provide an automobile driving system having a simple construction, comprising component parts common to various types, and, when designed for use on a two-wheel drive vehicle, capable of being readily modified for use on a four-wheel drive vehicle.